The solid-state chemical stability of a compound sometimes can be influenced by the selection of an appropriate salt form. However, there are no established general principles one can follow in improving solid-state stability through salt modification. For a review of information relating to the selection of "Pharmaceutical Salts" see S. M. Berge, et al., J. Pharm. Sci. 66, pp. 1-19 (1977).
The free acid of 6,9-deepoxy-6,9-(phenylimino)-.DELTA.6,8-prostaglandin I.sub.1 and related analogs are known compounds having utility as antiasthmatic agents. See, e.g., U.S. Pat. No. 4,294,759 issued Oct. 13, 1981. The compound of the present invention, i.e., the potassium salt of 6,9-deepoxy-6,9-(phenylimino)-.DELTA.6,8-prostaglandin I.sub.1, possesses a number of advantageous physical properties over the free acid rendering said potassium salt a markedly superior product candidate.